How to Import Old code from a Different namespace into My Current Project?

Question

I want to use old code in a new project in c#.

This is the old code. It is saved in an arbitrary folder on my PC.

namespace OldCode{
    class HellowWorld
    {
        public static void SayHello()
        {
            Console.writeline("Hello World")
        }
    }
}

I want to use this in a new project called new code.

using OldCode (?)

namespace NewCode
{
    class SayHelloNew
    {
        HelloWorld.SayHello();
    }
}

My question is, how do I link to my old project? Did I do it right with using OldCode? Or is there some other dependency file I need to set up?

Answer 1

That is almost correct. The colon ( : ) needs to be removed from the namespace declaration and to access the HelloWorld class externally, it must be public.

OldCode\HelloWorld.cs

namespace OldCode
{
    public class HelloWorld
    {
        public static void SayHello()
        {
            Console.writeline("Hello World")
        }
    }
}

NewCode\SayHelloNew.cs

using OldCode;

namespace NewCode
{
    class SayHelloNew
    {
        HelloWorld.SayHello();
    }
}

You will also need to ensure the compiler has access to OldCode on compilation, or, if using Visual Studio, add a Reference to the OldCode project in the NewCode project.

Add references in Visual Studio

Answer 2

Yeap, Let me describe for you,
First you should make public your class to access it in other sources by adding public modifier like this:

using System;
namespace Stackoverflow.OldCode
{
    public class HelloWorld    // <----------- make it public
    {
        public static void SayHello()
        {
            Console.WriteLine("Hello World!!!");
        }
    }
}

Then I suggest adding a prefix in every other namespace s to show they are related to each other, like

namespace Stackoverflow.OldCode;
namespace Stackoverflow.NewCode;

The NewCode project and the OldCode should be in one solution, if not now, right-click on the solution name and choose: Add>New Project... or Add>Existing Project...

Then you should add the NewCode project as a reference to the OldCode project:

step1:

step2:

Now you can access old project methods easily, like:

using Stackoverflow.OldCode;   // <---- add the reference
namespace Stackoverflow.NewCode
{
    class SayHelloNew
    {
        public static void SomeRandomName()
        {
            HelloWorld.SayHello();  // <----- call it 
        }
    }
}